Process hazelnuts in a food processor until finely chopped.

In the top of a double boiler over simmering water melt chocolates and butter, stirring until smooth and butter is thoroughly incorporated.

In a saucepan heat cream until hot but not boiling. Stir into melted chocolate little by little, stirring until completely incorporated between additions. Stir in hazelnuts and liqueur.

Serve in a fondue pot over a very low flame, with your choice of accompaniments.